People can indeed backslide and change their views as you see in life and around you you can also read many accounts of it in the old and new testament. But thankfully God is not like this and does not change:
"Jesus Christ is the same yesterday and today and forever." Hebrews 13:8 ESV
For this we should be thankful we have a rock to hold onto on which we can "build our house".
And so even though we are fickle God is not and therefore of whom God has called "...no one will snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand." John 10:28-29 ESV
Therefore, it is not possible for a Christian, one whom God has called, to fall away. I know one can doubt ones belief in God - I know I do sometimes (am I really a Christian? Am I kidding myself? Is it somehow not true?) - but then I remember that it is down to God that I am saved, not me!!
This is where faith in Jesus (being a Christian) is different. There are no good works or ceremonies or religion. Christianity is all about what God has done, is doing and will do and trusting in that! You will find it is the dusty old religious places that people are leaving and that are declining because they have turned faith into religion and many have drifted away from sound teaching. But in churches that put God in the centre rather than religion and that cleave to what scripture says - these churches are growing!